. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 318 METEOROLOGY AND ALLIED SUBJECTS. cloudiness appears to favor the development of certain auroras. As to the connection between the magnetic perturbations and the aurora, the observations show that perturbations of the needle may take place without the auroral display, and vice verm, the aurora without pertur- bations of the needle. Those forms of aurora that present irregular outlines, no rays, and no perceptible motions, are seldom acco
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 318 METEOROLOGY AND ALLIED SUBJECTS. cloudiness appears to favor the development of certain auroras. As to the connection between the magnetic perturbations and the aurora, the observations show that perturbations of the needle may take place without the auroral display, and vice verm, the aurora without pertur- bations of the needle. Those forms of aurora that present irregular outlines, no rays, and no perceptible motions, are seldom accompanied by perturbations: on the other hand those auroras that appear to have a small altitude, and to be very near to us, having definite outlines, rapid movements, and well-marked radial structure, set the needle in rapid movement. {Z. 0. 6. ill., XIY, 1879, p. 190.) P. F. Denza has given the following laws relating to atmospheric elec tricity, based on twelve years' observations—six times daily—at Mon- calieri: Regular variations.—He says the daily variations show them- selves clearly in the winter and summer, having two maxima after sunset and sunrise. The yearly variations attain their maxima at the end of February, the minima in September. The annual means show no connection with sun spots or magnetic changes. Irregular varia tions.—Thunder storms affect the tension very much. Eain and snow increase the electricity. Dense fog and haze, cloudiness, etc., increase the intensity very slightly. The least electricity is shown during clear or very clear sky, and especially when it is also very warm. Southerly winds, especially southeast, increase the electricity; but during strong winds the indications of the electrometer are uncertain. During these twelve years, out of a hundred cases of rain and snow, fifty give nega-^ tive and fifty positive electricity; the same ratio holds good for thun- der storms and hail, whether they pass over the observer or ])ass by at a dist
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